Technical Field
This technology relates to low porosity fibrous materials, articles formed therefrom and processes for their formation.
Description of the Related Art
High tenacity fibers, such as SPECTRA® polyethylene fibers or aramid fibers such as KEVLAR® fibers, are well known as useful for the formation of high performance articles, such as ballistic and impact resistant articles because of their very high strength to weight performance. Such articles formed from high tenacity fibrous tapes are also known. Articles formed from such high tenacity fibers also exhibit desirable properties such as good wear resistance, cut resistance and slash resistance at low fiber volumes.
For many applications, the fibers or tapes may be formed into woven or knitted fabrics. For other applications, the fibers or tapes may be encapsulated or embedded in a polymeric matrix material and formed into non-woven fabrics, such as unidirectional fabrics or felts. In one common non-woven fabric structure, a plurality of unidirectionally oriented fibers are arranged in a generally coplanar, coextensive relationship and coated with a binding matrix resin to bind the fibers together. Typically, multiple plies of such unidirectionally oriented fibers are merged into a multi-ply composite. See, for example, U.S. Pat. Nos. 4,403,012; 4,457,985; 4,613,535; 4,623,574; 4,650,710; 4,737,402; 4,748,064; 5,552,208; 5,587,230; 6,642,159; 6,841,492; and 6,846,758, all of which are incorporated herein by reference to the extent consistent herewith.
Despite the physical strength benefits of articles formed from such high tenacity fibers, these articles tend to have undesirable liquid transmission properties due to high porosity. This is a particular problem with woven fabrics wherein weft fibers are transversely disposed across and between longitudinal warp fibers in an undulating fashion. One way to solve this problem is to seal fabric pores by applying polymeric films or coatings to the fabric surfaces. However, this adds additional complexity to the fabrication process and increases fabric weight, which may be undesirable. Another means to address the problem of liquid transmission through a fabric is to minimize the space between adjacent fibers, such as by adding more fibers to a fibrous layer. However, that too will add weight to a fabric which is typically undesirable. A more preferred method of minimizing space between adjacent fibers is spreading filaments apart to form thinner fiber layers having fewer fibers that lie on top of each other. However, it is difficult to produce thin fabrics with sufficient mechanical integrity to be processed into articles when the filaments of the fibers are spread very thinly, particularly when fabricating unidirectional non-woven fabrics.
One method of addressing this problem of inadequate mechanical integrity during fabrication of unidirectional non-woven fabrics is to use a release paper carrier sheet during processing. In a typical process, an array of unidirectionally oriented parallel fibers is coated with a binder resin and then the coated fibers are contacted with a silicone-coated release paper while the resin is still wet. The coating is then dried and the release paper is removed. However, this method is imperfect because it is desired to avoid the use of a carrier sheet in the manufacturing process and it is also desirable to avoid the need for a binding resin.
U.S. Pat. No. 8,349,112 teaches a method of weaving polymeric tapes together with binding threads, with the polymeric tapes being used as warp yarn and a binding thread being used as weft yarn or with the polymeric tapes being used as weft yarn and a binding thread being used as warp yarn, followed by consolidating multiple layers with sufficient heat to melt the binding threads. The melting deforms the binding threads, distributing the resin around the non-melted polymeric tapes, thereby acting as an adhesive coating. This eliminates the undulations caused by the weaving process. However, this method does not produce articles having less than 10% resin content with sufficient mechanical integrity. U.S. Pat. No. 8,349,112 is silent with regard to binding resin content, but the thermal destruction of the binder fibers compromises the fabric breaking strength in the direction transverse to the polymeric tapes. The melting of the binder fibers also eliminates the mechanical interlocking of warp and weft fibers created by the weaving process, resulting in a non-woven fabric with the binder polymer serving as a conventional adhesive coating. This resulting fabric either has greater than 10% resin content or less than 10% resin content and inadequate mechanical integrity, thereby failing to improve upon prior art composites. Accordingly, U.S. Pat. No. 8,349,112 fails to achieve the objectives of the present disclosure.
U.S. Pat. No. 4,680,213 teaches structures where non-thermoplastic, reinforcing textile yarns are bonded by adhesion with binding yarns disposed transverse to the textile yarns. The reinforcing textile yarns are spaced apart from each other and the binding yarns are spaced apart from each other, so as to form permanent holes in their laminates. This type of open structure is unacceptable for water resistant fabric applications as are desired herein.
Accordingly, there is an ongoing need in the art for lightweight, low porosity woven and non-woven fabrics having good mechanical integrity with low or no binding polymer content and wherein the use of surface polymeric films is optional. The present disclosure provides a solution to this need.